The present invention relates to magnetic recording media, and more particularly is a modulated grain-composition magnetic media system with up to terabit areal density recording capacity which, in preferred practice is produced by sequential multiple layer vacuum deposition, and subsequent annealing, procedures that allow selective fabrication of magnetic recording materials with intended grain size and coercivity, with longitudinal or perpendicular magnetic particle xe2x80x9cc-axisxe2x80x9d orientation.
As reported in an article by Wood, titled xe2x80x9cThe Feasibility of Magnetic Recording at 1 Terabit Per Square Inchxe2x80x9d, IEEE Transactions of Magnetics, Vol. 36, No. 1, (January 2000), areal density, (ie. bits per square inch), in magnetic recording products has grown at a rate approaching 100% per annum, (with practical systems now operating at an areal density of 1010 bits per square inch). Said article, which is incorporated by reference hereinto, also projects that in view of ultimate practical limitations in realizable magnetic read-write system heads, an ultimate-utility providing magnetic recording material can be described as one which presents with a maximum Coercivity (Hc) of approximately twelve Kilo-Oersteds (12K-Oe) based on perpendicularly oriented magnetic particles which have an associated minimum grain size diameter of just under ten (10 nm) nanometers, (ie. minimum stable grain size volume of six-hundred (600) cubic nanometers). Said paper further makes clear that while magnetic media with smaller grain size and larger Coercivities (Hc) are very achievable, thermal stability and practical ultimate magnetic head writing capability provide the recited grain size and Coercivity (Hc) values as representing theoretically xe2x80x9coptimumxe2x80x9d in unpatterned magnetic recording media.
In view of the fact that presently marketed magnetic recording system technology typically utilizes longitudinally xe2x80x9cc-axisxe2x80x9d oriented magnetic particle containing materials which demonstrate maximum Coercivities (Hc) on the order of three (3K-Oe) to four (4K-Oe) Kilo-Oersteds, it can be concluded that a magnetic recording material which would provide a minimum grain size of around ten (10) nanometers and a maximum Coercivity (Hc) of approximately twelve (12K-Oe), but which would allow adjustment of maximum Coercivity (Hc) downward by controllable and known fabrication parameters, and which magnetic recording material could be fabricated to demonstrate either longitudinal or perpendicular magnetic particle xe2x80x9cc-axisxe2x80x9d orientation therewithin, again by control of known fabrication parameters, would provide not only immediate utility, but utility projected into the far foreseeable future when practical fabricated magnetic recording system write head system capabilities approach upper theoretical limitations.
The inventors of the present invention have identified several nanocomposite material containing films with potential for application in extremely high-density magnetic recording materials, including CoPr, CoPt, CoSm, SmFeSiC SmFeAlC and FePt. (See xe2x80x9cNanoscale Design of Films for Extremely High Density Magnetic Recordingxe2x80x9d, Sellmyer, Yu, Thomas, Liu and Kirby, Phys. Low-Dim. Struct., xc2xd155, (1998)).
The present inventors have also observed that various materials demonstrate relaxed viscosity at temperatures of, for instance:
xe2x80x831446 K for SiO2;
820 K for GeO2;
526 K for B2O3;
186 K for Glycerol;
(see for instance xe2x80x9cDynamics of Strong and Fragile Glass Formers: Differences and Correlation with Low-Temperature Propertiesxe2x80x9d, Sokolov et al., Phys. Rev. Lett, Vol. 71, No. 13, p. 2062, (1993)).
The conceptual insight leading to the present invention, was that magnetic recording material systems which combine alternating layers of appropriate thicknesses of:
nanocomposite material containing films; and
films of materials which demonstrate relaxed viscosity at desirable anneal temperatures;
might allow fabrication of magnetic recording materials which demonstrate predictable magnetic material grain size, predictable maximum coercivity (Hc) and magnetic particle xe2x80x9cc-axisxe2x80x9d orientation, (ie. longitudinal or perpendicular to a resulting magnetic recording material film), by a relatively simple multi-layer vacuum deposition, (and subsequent anneal), procedure onto even non-lattice matched substrates.
It is noted at this point that other researchers have reported fabrication of FePt films on lattice matched (001) MgO single crystal substrates using Molecular Beam Epitaxy (MBE) systems. Articles describing this are;
xe2x80x9cDirect Formation of Ordered CoPt and FePt Compound Thin Films by Sputteringxe2x80x9d, Visokay and Sinclair, App. Phys. Lett., 66, (1995);
xe2x80x9cEnhanced Magneto-Optical Keer Effect in Spontaneously Ordered FePt Alloys: Quantitative Agreement Between Theory and Experimentxe2x80x9d, Cebollada et al., Phys. Rev. B, 50 (1994).
xe2x80x9cControl of the Axis of Chemical Ordering and Magnetic Anisotropy in Epitaxial FePt Filmsxe2x80x9d, Farrow et al., J. App. Phys. 79 (1996).
The films achieved present with perpendicularly oriented xe2x80x9cc-axisxe2x80x9d orientation. Said approach again, however, requires (MBE) capability and use of lattice matching (001) MgO.
Inventors of the presently disclosed invention have investigated fabrication of longitudinally oriented magnetic recording media with a coercivity of 3000 Oe to 6300 Oe, as described in Patent to Sellmyer et al., U.S. Pat. No. 5,824,409. Said 409 Patent describes production of said a magnetic recording media composed of alternating thin film layers of Platinum (Pt) and an element selected from the group consisting of Iron (Fe) and Cobalt (Co), sequentially deposited onto a substrate. To achieve the final system result an anneal of the deposited materials at 300 to 600 degrees Centigrade was performed.
Previous published results by the present Inventors has documented fabrication and investigation of Co:C; CoPt:C, Fe/Pt; FePt:SiO2 films. Said work is variously described in Scientific Articles:
xe2x80x9cStructural and Magnetic Properties of Nanocomposite Co:C Filmsxe2x80x9d, Yu, Liu and Sellmyer, J. App. Phys. Vol. 85, No. 8, (Apr. 15, 1999);
xe2x80x9cNanocomposite CoPt:C Films For Extremely High-Density Recordingxe2x80x9d, Yu, Liu, Weller and Sellmyer, App. Phys. Lett., Vol. 75, No. 25, (Dec. 20, 1999);
xe2x80x9cMagnetic Viscosity and Switching Volumes of Annealed Fe/Pt Multilayersxe2x80x9d, Luo, Shan and Sellmyer, J. App. Phys. 79(8), (Apr. 15, 1996);
xe2x80x9cMagnetic Properties and Structure of Fe/Pt Thin Filmsxe2x80x9d, Luo and Sellmyer, IEEE Transactions on Magnetics, Vol. 31, No. 6, (November 1995); and
xe2x80x9cStructural and Magnetic Properties of FePt:SiO2 Granular Thin Filmsxe2x80x9d, Luo and Sellmyer, App. Phys. Lett., Vol 75, No. 20, (Nov. 15, 1999).
A further paper by present Inventors is titled xe2x80x9cNanostructured Magnetic Films For Extremely High Density Recordingxe2x80x9d, Sellmyer, Yu and Kirby, Nanostructured Mat., Vol. 12, (1999). This paper reports that over twenty years coercivity (Hc) in Co-based recording media has increased for approximately 0.3 K-Oe to approximately a present 3K-Oe and that the most advanced media presently are CoCrPtX alloys, where X represents Ta, Nb etc.
A Search of Patents has identified a Patent to Sellmyer et al., U.S. Pat. No. 5,824,409 which focuses on longitudinal high coercivity recording media comprised of alternating layers of Fe and Pt, without mention of intervening Oxide layers therebetween, however.
A recent U.S. Pat. No. 6,183,606 B1 to Kuo et al., describes FePt-Si3N4 composite films. This Patent does not claim perpendicular anisotropy, nor does it describe simultaneously obtaining both high coercivity (eg. 8-11 kOe) and small grain size (eg. 8 nm). Said 606 Patent does provide a thin film for magnetic recording media including particles of about 50 nm diameter, 200 nm thickness, high coercivity, plane-parallel easy axis, FePt at 50/50 proportions, and fcc crystal phase going into fct phase during anneal at near 600 degrees Centigrade. However, the matrix in which the FePt particles reside comprises Si3N4 which is a non-magnetic phase serving the simple role of diluting the magnetism of the material. Other materials are not disclosed to serve as the non-magnetic phase.
A U.S. Pat. No. 5,603,766 to Visokay et al. describes a method for producing uniaxial tetragonal thin films of ternary intermetallic compounds. Preferably the substrate is single crystal, such as MgO or Al2O3, or an amorphous material such as SiO2, amorphous carbon or glass. A sequence of three metals are deposited with the substrate heated to 450 degrees Centigrade. The first and second metals are selected from the group (CoNi or CoFe or FeNi), and the third metal is Fe or Pt. The thin film formed is a ternary intermetallic compound exhibiting an Li0 crystal structure and uniaxial properties.
A U.S. Pat. No. 5,363,794 to Lairson et al. describes uniaxial thin films formed from multilayers of Fe and Pt on MgO. Annealing at 450 degrees Centigrade is conducted after sputter deposition.
Even in light of existing art, it should be appreciated that films of magnetic materials, (eg. FePt/Oxide or Fe/Pt/Oxide), with up to terabit areal density recording capacity, which are, in preferred practice, produced by relatively simple sequential vacuum deposition and annealing procedures that allow selective control of magnetic material grain size, coercivity and/or magnetic particle longitudinally or perpendicularly oriented xe2x80x9cc-axesxe2x80x9d, would provide utility. With this in mind, it is disclosed that the present invention identifies FePt and/or Fe/Pt based materials, (eg. FePt/SiO2 and FePt/B2O3, Fe(Co)Pt/SiO2 and Fe(Co)/B2O3), with FePt/B2O3 as preferred, and discloses relatively simple fabrication methodology therefore.
References identified in the Background Section of this Specification disclose that it is known that equiatomic FePt alloy films with an (fct) tetragonal Llo structure are characterized by a very high anisotropic energy constant (K1) on the order of 7xc3x97107 erg/cc, which makes them very attractive for application in recording media with an areal density of 100 Gbit per square inch and higher. Further, based on thermal stability considerations, it is known that an ultimate optimum grain size in equiatomic FePt alloy films with an (fct) tetragonal Llo structure is on the order of just under 10 nm.
It must be appreciated however, that while theoretically optimum magnetic recording material parameters are known, presently available recording systems can not yet write to media which optimally have, for instance, a Coercivity of about twelve (12) K-Oe. Hence, at least until more optimum write, and read, capability is realized, magnetic media characterized as less than theoretically optimum will continue to find application. It is noted that presently Coercivity (Hc) in typical magnetic media which can be written onto by existing magnetic recording system write heads is on the order of 3-4 K-Oe.
In that light, it becomes apparent that a need exists for magnetic recording media, and specific methodology of its fabrication, which allows predictably and routinely realizing magnetic recording media with intended magnetic material grain size and coercivity (Hc) and magnetic particle xe2x80x9cc-axisxe2x80x9d orientation. Were such a magnetic recording media and fabrication methodology available it would provide great utility, both immediately and into the foreseeable future. The present invention answers said need in the form of, in the preferred embodiment, identifying multi-layer FePt/Oxide, (where B2O3 is the preferred oxide), magnetic media, and fabrication methodology therefore based in vacuum deposition and anneal. Briefly, control of FePt or Fe/Pt layer and/or Oxide layer thickness, and/or annealing temperatures and times, during fabrication enables realization of magnetic media with selected, (albeit correlated), grain size and coercivity values, and with longitudinal or perpendicular magnetic particle xe2x80x9cc-axisxe2x80x9d orientations.
The preferred embodiment of the present invention system then can be recited as being a magnetic media suitable for use in extremely high density recording systems, comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and Oxide;
layers on a surface of a substrate. What distinguishes said system is that it is characterized by an X-ray diffraction pattern wherein a (111) peak has a magnitude between substantially absent and less than half the magnitude of the larger of present (001) and (002) peaks. A preferred oxide is selected from the group consisting of:
SiO2; and B2O3;
(with B2O3 being most preferred), and the order of the substrate and at least one FePt and at least one Oxide layers, is selected from the group consisting of:
substrate-FePt and/or Fe/Pt-Oxide; and
substrate-Oxide-FePt and/or Fe/Pt.
Said system can be fabricated by, in any functional order, the steps of:
a. providing a substrate;
b. providing a vacuum deposition system comprising sources of FePt and/or Fe and Pt and an oxide;
c. placing said substrate into said vacuum deposition system;
d. depositing a plurality of sequentially alternating layers, in an order selected from the group consisting of:
FePt/Oxide;
(Fe/Pt)/Oxide
Oxide/(Fe/Pt)
Oxide/FePt;
onto said substrate; and
e. annealing said substrate onto which has been vacuum deposited a plurality of sequentially alternating layers of:
FePt and/or Fe/Pt; and Oxide;
at a temperature and time combination sufficient to result in a system characterized by an X-ray diffraction pattern wherein a (111) peak has a magnitude between substantially absent and less than half the magnitude of the larger of present (001) and (002) peaks.
In the preferred embodiment the preferred oxide is selected from the group consisting of:
xe2x80x83SiO2; and B2O3,
To realize the alternative embodiment, said FePt layer(s) are deposited to be less than about forty Angstroms thick.
A preferred present invention system can be recited as a magnetic media suitable for use in extremely high density recording systems, comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and B2O3;
layers on a surface of a substrate wherein said FePt layer(s) are less than forty Angstroms thick, said system being characterized by an X-ray diffraction pattern wherein a (111) peak has a magnitude between substantially absent and less than half the magnitude of the larger of the (001) and (002) peaks. Said system B2O3 layer is typically selected to be between eight (8) and twelve (12) Angstroms thick and the system presents with a coherence of between ten thousand (10,000) and twelve thousand (12,000) Orsteds.
An important consideration is that the method of fabricating a present invention system does not require providing a substrate which is essentially lattice matched to crystallinity of the resulting magnetic recording material and a suitable substrate, it is noted, is 7059 glass.
An alternative embodiment of a present invention system can be recited as a magnetic media suitable for use in extremely high density recording systems, comprising a plurality of sequentially alternating,
xe2x80x83FePt and/or Fe/Pt; and B2O3;
layers on a surface of a substrate wherein said FePt or (Fe/Pt) layer(s) are greater than about forty Angstroms thick, said system being characterized by an X-ray diffraction pattern including (110) and (220) peaks and essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) peaks.
Said alternative embodiment of a present invention system can be fabricated by, in any functional order, the steps of:
a. providing a substrate;
b. providing a vacuum deposition system comprising sources of FePt and/or Fe and Pt and an oxide;
c. placing said substrate into said vacuum deposition system;
d. depositing a plurality of sequentially alternating layers, in an order selected from the group consisting of:
FePt/Oxide;
(Fe/Pt)/Oxide
Oxide/(Fe/Pt)
Oxide/FePt;
onto said substrate; and
e. annealing said substrate onto which has been vacuum deposited a plurality of sequentially alternating layers of:
FePt and/or Fe/Pt; and Oxide;
at a temperature and time combination sufficient to result in a system characterized by an X-ray diffraction pattern including (110) and (220) peaks and essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) peaks, after the anneal procedure.
Said alternative embodiment preferable involves providing an oxide selected from the group consisting of:
Sio2; and B2O3.
To realize the alternative embodiment, said FePt layer(s) are deposited to be greater than about forty Angstroms thick.
A preferred alternative system embodiment comprises a plurality of sequentially alternating,
FePt and/or FePt; and B2O3;
layers on a surface of a substrate wherein said FePt layer(s) are less than forty Angstroms thick, said system being characterized by an X-ray diffraction pattern including (110) and (220) peaks with essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) peaks, after the anneal procedure after the anneal procedure, and the B2O3 layer is between eight (8) and twelve (12) Angstroms thick and the system presents with a coherence of between six (6) thousand (6,000) and twelve thousand (12,000) Oersteds.
Again, particularly where B2O3 is the oxide present, it has been determined that where as-deposited FePt layer(s) are less than about forty (40) Angstroms thick appropriate annealing tends to cause as-deposited films to undergo a phase transition from FePt face-centered-cubic (fcc) to a face-centered-tetragonal (fct) structure which demonstrates (001) and (002) X-ray Diffraction peaks of significant magnitude, with concurrent reduction of the (111) XRD peak. Where as-deposited FePt layer(s) are greater than about forty (40) Angstroms thick appropriate annealing tends to cause as-deposited films to undergo a phase transition from FePt face-centered-cubic (fcc) to a face-centered-tetragonal (fct) structure which demonstrate (110) and (220) peaks and essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) X-ray diffraction peak magnitudes after anneal.
Where B2O3 is the oxide utilized in a present invention system, it has been found that annealing at 550 degrees Centigrade for 30 minutes cause as-deposited films to undergo a phase transition from FePt or Fe/Pt face-centered-cubic (fcc) to a face-centered-tetragonal (fct) structure.
Where SiO2 is the oxide utilized in a present invention system, it has been found that annealing at between 450 and 650 degrees Centigrade for up to 2 hours causes as-deposited films to undergo a phase transition from FePt face-centered-cubic (fcc) to a face-centered-tetragonal (fct) structure. In addition, rapid thermal annealing (RTA) can be applied, such as wherein temperature is increased at 100 degrees Centigrade per second, then held constant for one second, then cooled over a period of ten seconds.
The methodology of fabricating any present invention system typically involves providing a vacuum deposition system within which is caused to be a base pressure of about 10xe2x88x927 Torr therewithin, prior to entry of argon to a pressure of about 5 m-Torr and vacuum sputtering deposition of said alternating layers of FePt and/or Fe/Pt and Oxide.
It is specifically to be understood that while the methodology of fabrication involves deposition of alternating layers of Fe Pt and Oxide, after anneal the present invention system comprises modulated granular composition rather than clear, sharply defined, layers.
The present invention will be better understood by reference to the Detailed Description Section of this Specification, with reference to the accompanying Drawings.
It is therefore a primary purpose and/or objective of the present invention to teach a system comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and Oxide;
layers on a surface of a substrate, said system being characterized by an X-ray diffraction pattern wherein a (111) peak has a magnitude between substantially absent and less than half the magnitude of the larger of present (001) and (002) peaks; said system being a magnetic media suitable for use in extremely high density recording systems;
wherein the oxide can be SiO2, but is preferably B2O3; and
wherein the FePt layer(s) thickness is less than about 40 Angstroms.
It is another primary purpose and/or objective of the present invention to teach fabrication of a system comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and Oxide;
layers on a surface of a substrate, said system being characterized by an X-ray diffraction pattern wherein a (111) peak has a magnitude between substantially absent and less than half the magnitude of the larger of present (001) and (002) peaks; said system being a magnetic media suitable for use in extremely high density recording systems;
by vacuum deposition onto a non-lattice matched substrate, and anneal, procedures.
It is yet another purpose and/or objective of the present invention to teach a system comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and Oxide;
layers on a surface of a substrate, said system being characterized by an X-ray diffraction pattern including (110) and (220) peaks and essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) peaks after anneal; said system being a magnetic media suitable for use in extremely high density recording systems; and
wherein the oxide can be SiO2, but is preferably B2O3; and
wherein the FePt layer(s) thickness is greater than about 40 Angstroms.
It is another purpose and/or objective yet of the present invention to teach fabrication of a system comprising a plurality of sequentially alternating,
FePt and/or Fe/Pt; and Oxide;
layers on a surface of a substrate, said system being characterized by an X-ray diffraction pattern including (110) and (220) peak and essentially negligible (111), (001) and (002) peaks which are less than half the larger of the (110) and (220) peaks after anneal; said system being a magnetic media suitable for use in extremely high density recording systems;
by vacuum deposition onto a non-lattice matched substrate, and anneal, procedures.
It is a further purpose and/or objective of the present invention to provide insight to fabrication methodology for tailoring production of magnetic media with desired coercivity, grain size and longitudinal or perpendicular particle orientation.
Other purposes and/or objectives of the present invention will be apparent from a reading of this Specification.